Field of the Invention
The present invention relates to a charging device which charges a photosensitive drum, to a process cartridge having this charging device, and to an image forming apparatus provided with this process cartridge.
Related Art
In the prior art, electrophotographic type image forming apparatus use a charging device for uniformly charging the surface of a photosensitive drum as an image support body, and as such a charging device, scorotron charging devices have been known.
A scorotron charging device is provided with a discharge electrode which carries out corona discharge for the photosensitive drum and charges the photosensitive drum, a grid electrode for controlling the amount of the charge applied to the surface of the photosensitive drum by the discharge electrode, and a shield case in which they are housed; wherein the grid electrode can almost accurately control the charging potential of the surface of the photosensitive drum, and as a result it is widely used as a charging device for a photosensitive drum.
Particularly, a scorotron charging devices combining a grid electrode of a porous plate shape where a plurality of through-holes are formed with a mesh shape or slit shape on a metal plate (grid substrate) consisting of stainless steel or the like, and discharge electrodes having a plurality of acutely shaped protruding portions have attracted attention because they have little adhesion of dirt to the grid electrode and they can uniformly charge the surface of the photosensitive drum, and various improvements have been proposed (for example, refer to Patent Document 1).
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2009-251310